The invention relates to a method for the real-time monitoring of tire pressure on a motor vehicle, wherein the pressure reading determined by use of a pressure sensor arranged in the tire is transmitted in brief transmission intervals by an electronic wheel device, via radio and without using a trigger transmitter fixed in the vehicle, to a monitoring device installed in the vehicle, at least when the vehicle is not moved, and only when the pressure reading is outside of a prespecified normal range. By way of example, the prior art includes DE 102 13 266 A1.
Today, systems for monitoring the air pressure in vehicle tires are already used in passenger vehicles. These systems measure the pressure in the tire and telemetrically transmit, meaning via radio, the measured values to a monitoring device installed in the vehicle. The electronic wheel device currently used for this purpose is designed to transmit a so-called telegram when the vehicle is moving at a speed above a threshold value of, by way of example, 15 km/h, wherein this speed can be determined by an acceleration sensor integrated into the electronic wheel device, in short intervals of time. The telegram typically contains information about the transmitter, particularly the so-called identification number, and also the current value for the pressure and the temperature of the air in the tire. Typically, a transmission time on the order of 5 milliseconds to 20 milliseconds is required. The electrical batteries integrated into the electronic wheel devices in this case are designed to provide the electrical power needed for this function over a period of approximately 10 years.
Before the electronic wheel devices described in the previous paragraph came into use, such electronic wheel devices installed in the tire only transmitted the measured pressure value to a monitoring device installed in a fixed position in the vehicle after receiving a trigger signal, which trigger signal was sent by a transmission device installed on the vehicle near to the respective tire.
In several different countries, there is a requirement by law that the air pressure in the tire is monitored immediately upon start-up of the vehicle, and if an unacceptable tire pressure is detected, the driver is to be notified of this, wherein it is not necessary to make the vehicle move for this purpose. Because, therefore, a pressure monitoring must be carried out when the vehicle is stationary, it is not possible to use the system as briefly described above, which is currently in use. This system could be modified in such a manner that the measured tire pressure is transmitted to the monitoring device continuously, meaning even when the vehicle is stationary, and particularly even when the vehicle has not even been started—but then it is not possible to even come close to achieving the required life span of the batteries which power the electronic wheel device, said life span being approx. 10 years. In addition (more theoretically), the earlier system mentioned above having the trigger transmitter could be used, wherein the electronic wheel device can be implicitly informed of the vehicle being started by corresponding trigger signals being transmitted only when the vehicle has been started, wherein the electronic wheel device would consequently thereby need to be used much less frequently (and therefore would require significantly less electrical energy). However, this would involve relatively high cost and effort.
Also known from DE 102 13 266 A1 is the approach of transmitting at least a part of the detected tire pressure measured value with a modifiable frequency to a receiving device, which in the present case is a monitoring device, wherein the frequency of the transmission of the tire pressure measured value is derived from the detected tire pressure measured value itself. In this case, it is possible to not transmit all of the measured values detected by the transmission device installed in the tire and/or wheel of the vehicle, as long as the detected tire pressure measured value is in a normal range. In this way, it is possible to significantly reduce the energy consumption of the transmission device; however, it has been shown that it is not yet possible, with a reasonable design of this system, which ensures the desired battery life span, to obtain a valid declaration, substantially immediately upon start-up of the vehicle, about the functional security of the tire pressure monitoring system, and particularly about the accuracy of the tire pressure and/or optionally a defectiveness thereof, after a longer period during which the vehicle has been stationary.
Therefore the problem addressed by the invention is that of providing a method which is suitable, while using the conventional electric batteries, to monitor the tire pressure in real-time over the required operating life of approx. 10 years, by way of example, without a trigger transmitter which is fixed on the vehicle being necessary. The term “real-time monitoring” in this case, in the context of a tire pressure monitoring system, means a tire pressure monitoring system which is capable of real-time monitoring which will be required in the future by law in several countries, and by means of which warnings relating to a tire overpressure, a tire low pressure or a system failure are displayed to the driver or the user of the vehicle within a few seconds. In this case, it is also required that the driver is immediately informed within a few seconds upon start-up of the vehicle, while the same is still stationary, by means of a very quick announcement, of a system failure or of inadequate tire pressure in a tire.
The solution to this problem consists of a method for the real-time monitoring of the tire pressure in, particularly, a motor vehicle, wherein the pressure value determined by use of a pressure sensor included in the tire is transmitted by an electronic wheel device, without the use of a trigger transmitter fixed on the vehicle, by radio, in short transmission intervals, to a monitoring device installed in the vehicle, only if—at least when the vehicle is not moving—the value is outside a prespecified normal range. In contrast, when the vehicle is not moving, the electronic wheel device transmits a signal which is at least suited for the system monitoring function, at certain intervals, said signal having a short transmission duration on the order of 25 μs to 500 μs, and using the same time frame, or a whole-number fraction or multiple thereof, and carries out a measurement of the tire pressure. Advantageous implementations are described and claimed herein. In addition, features of a device for carrying out the method according to the invention are described and claimed herein.
In order to make it possible to enable the required real-time monitoring in a simple manner and over many years, without an exchange of the electrical batteries integrated into the electronic wheel device, the composite functions, as fundamentally required in a tire pressure monitoring system and in systems which are conventional at this time, of a system and transmission path monitoring, on the one hand, as well as the monitoring of the tire pressure on the other hand, are divided in such a manner that each of these two functions are optimized while fulfilling the named real-time requirements with respect to the energy consumption thereof. In this regard, at least one signal which serves the purpose of monitoring the system and the transmission path is effectively continuously—meaning repeatedly in short time intervals—transmitted to the monitoring device installed in the vehicle, while a signal which transmits the tire pressure is only transmitted, when the vehicle is stationary, if the tire pressure is outside of its prespecified normal range in any way. Of course, the pressure in the tire is likewise measured in this effectively continuous manner, but the measured values are only transmitted, at least when the vehicle is not in motion, if these values are abnormal. A first check of whether the measured pressure values are in the normal range or outside of the same is therefore carried out according to the invention in the electronic wheel device itself, at least when the vehicle is not in motion.
The advantage of this division of functions is that the short transmission of a system monitoring signal requires significantly less electrical energy than the energy-consuming transmission of a measured pressure value, and typically also of a signal which represents, is indicative of, or transmits a measured temperature value. Because the time-frame in which a vehicle is not moving is typically significantly larger than the time-frame in which the vehicle is moving, it is possible with the method according to the invention to already significantly reduce the consumption of electrical energy in the electronic wheel device if the method is only carried out when the vehicle is stationary. The energy consumption of the electronic wheel devices can, of course, be further reduced if the method here is carried out fundamentally—meaning when the vehicle is in motion as well. In this case, signals are also transmitted, when the vehicle is in motion, by the electronic wheel device, in principle in short transmission intervals, said signals serving the purpose of system monitoring, while the measured tire pressure values (and the temperature values of the air in the tire, which will be addressed in greater detail at a later point) are only transmitted if the pressure values are outside of a prespecified normal range. Whether the vehicle is stationary or is in motion can be determined in this case preferably as has been done conventionally up to this point—by use of an acceleration sensor integrated into the electronic wheel device. However, as an alternative, this can be performed by use of other sensors suitable for the same—for example based on the deformation of the tire in the so-called tread area.
The present invention therefore exploits the knowledge, as discussed above, that the majority of the electrical energy required by an electronic wheel device of a tire pressure monitoring system is consumed by the radio transmitter of this device, while the actual measurements of pressure, and typically also the temperature of the air in the tire, only consume a fraction of the energy required for the transmission. In addition to this known fact, in the present case there is a difference regarding the information which is transmitted by radio. According to the invention, a relatively long, and therefore energy-wasting information transmission is restricted to few situations, at least when the vehicle is not in motion, and only takes place if an abnormality is detected. In contrast, an extremely short information transmission for the purpose of monitoring the system function requires very little energy, and can and/or should therefore occur regularly and frequently even when the vehicle is not in motion. A signal in this respect particularly only requires an extremely short transmission duration, on the order of 25 microseconds to 500 microseconds, according to how high the requirement is set with respect to susceptibility to failure.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawing.